Page describing how to use syntaxes for sign guis.
What are sign GUIs?
GUIs with the same UI when placing a sign, you can know them from Hypixel for example.
How to open sign GUI?
effect: open [new] sign[ ]gui with text %strings% type %itemtype% to %players%
You can use all types of signs (oak sign, birch sign, etc.). You can't use colorful text in it, it's unfortunally a limitation of Minecraft.
Example: open new signgui with text "", "===============", "TYPE NEW NICKNAME", "===============" type birch sign to player
How to get output from sign GUI?
event: on sign GUI update:
event values: player, line-%integer%
Example: on sign gui update: broadcast "%player% - %line-1%, %line-2%, %line-3%, %line-4%